Method of preparing pulp for the production of insulating board and the like



May 29, 1962 SUNG H. CHA 3,036,949 METHOD OF PREPARING PULP FOR THEPRODUCTION oF INSULATING BOARD AND THE LIKE Filed Aug. 21, 1959IIIIIII'IIIIII BY gwwmv ATTORNEY States 3,036,949 Patented May 29, 19623 oss 949 METHoD oF PREPAriIN PULP Fon Tim Pao- DIrIrroN oF INSULATINGoARn AND THE L This invention relates to the preparation of fibrouspulp, and more particularly, the preparation of pulp suitable especiallyfor the manufacture of fiber insulating board.

In its more specific aspects, the invention relates to and will hereinbe described with reference to production of such pulp from non-woodycellulosic fiber material such as bagasse. As will be seen, however, theprinciples of the invention may be adapted also to the treatment ofcoarse fibrous material produced from wood.

In the preparation of pulp suitable for the manufacture of relativelythick fibrous products, such as insulating board, lfrom sugar-canebagasse, it has long been the conventional practise to subject the rawbagasse rst to digestion in a chemical pulping liquor, such as anaqueous solution of soda ash, for several hours at temperaturesconsiderably above 212 F., and at corresponding steam pressures. Uponcompletion of this chemical digestion step, the bagasse is thensubjected to grinding, as in a Bauer grinder or grinders, followed byreiining, screening and washing of the pulp and forming a stock ofdesired consistency for felting the same into relatively thick sheets.

The principal object of the present invention is to provide a method ofpulping raw bagasse or other fibrous material by a procedure whichavoids the need for high temperature digesting or cooking of thematerial. Thus, by the present invention, the cost and upkeep of, andthe labor required for operating, the digesting equipment areeliminated, as is also the cost of generating the steam required for itsoperation.

Another object of the invention is to provide a process of theabove-described character, wherein raw bagasse or the like, treatedaccording to the invention, is as readily susceptible to grinding andrefining by the conventional pulp grinding and refining machines as isbagasse cooked or digested according to the processes now in use.

Still another object of the invention is to provide a process asaforesaid, capable of yielding a fibrous stock having a freeness andothercharacteristics such that it may be formed into relatively thicksheets on standard board-forming machines at substantially the samespeeds as in the case of stock prepared from pulp obtained with theconventional cooking or digesting of the raw material.

The adoption and increasing use, in recent years, of mechanical, inplace of manual, methods of harvesting sugarcane, has given rise to anumber of troublesome problems in the use of the sugar-extracted bagasseas raw material for the production of fibrous pulp. When sugarcane ismechanically harvested, the bagasse delivered from the sugar mills tothe pulp mills is unavoidably intermixed with considerable and varyingamounts of gritty rock (this being mainly of volcanic origin in the caseof sugar mills located in Hawaii), metallic particles, and otherabrasive substances. These abrasive materials present in the raw bagassecause excessive Wear and tear upon the equipment, such as the grinders,refiners, pumps etc., through which the material must pass in order toproduce the desired pulp from the bagasse, as well as upon the saws usedfor trimming board made from the pulp. In terms-of actual experience inthe production of board from bagasse obtained from mechanicallyharvested sugar-cane, it may be stated that the cost of labor andmaterial for repair and replacement of parts of such equipment amountsto from 30 to 35 cents per 1000 square feet of board (1/2 inch basis)more than the cost thereof in the case of bagasse obtained from manuallyharvested sugar-cane. Aside from this considerable increase in cost ofproduction of the board, the abrasive rock or the like present at oradjacent the bottom surface of board that is made with a paint coatingon its other surface, as in the case of so-called decorative tile oracoustical board, causes objectionable scratching of the paint coatingwhen the opposite surfaces of the boards are in moving contact with oneanother during subsequent handling in manufacture, storage and shipment.

Accordingly, it is still another object of the invention to provide aprocess of the character above-described, and which will make possiblethe removal of such rock or other abrasive substance from the bagassebefore it is subjected to the grinding and subsequent stages oftreatment for the production of pulp therefrom.

Brieiiy, according to the invention, the raw fibrous material, such asbagasse delivered from sugar mills, is subjected to treatment withchemical, such as soda ash, byl

soaking the same for a relatively short period of time in an aqueoussolution of the chemical at ambient atmospheric temperature and then,after removing excess water from the soaked material, allowing thematerial to age in quiescent state while arranged in a relatively deeplayer or layers thereof, for a period of time varying from about 40 toabout 100 hours. At the conclusion of the ageing period, the treatedmaterial may be fed directly and in constant amount to conventionalgrinders, following which the pulp may be refined in conventionalrefiners.

Within the broad range of time above indicated for ageing the bagasse,the preferred range will in most cases be from about 50 to about 75hours.

For the purpose of ageing the material in accordance` with theinvention, it may be piled in a warehouse o r other enclosed storagespace, to a depth of anywhere from, say, two to twenty feet or more.

By thus ageing the material after it has been substantially completelysoaked in the soda ash or other suitable chemical, the necessity forusing digesters or similar equipment for high temperature cooking of theraw material, and, consequently, the problems attendent thereon, areeliminated.

It has heretofore been proposed to produce paper making pulp from rawfibrous material, by treatments which do not require the use ofdigesters or cooking equipment. Such proposals are set forth, forexample, in patents to Traquair 1,936,697 and Vazquez 1,876,522. Theseprior processes contemplate, as in the case of Traquair, thesimultaneous mechanical disintegration of the fiber as by passing woodchips through a multi-stage rod-milling treatment together with caustictreating liquor; or, as in the case of Vazquez, the complete submersionof the rawl fibrous material, such as bagasse, in the treating solutionand allowing it to remain therein for a period of three to four months.So far as I am aware, none of such prior processes contemplates, orsecures the advantages obtainable by, a treatment of the raw materialwhich comprises, essentially, soaking it for a short time in an aqueoussolution of the chemical, and then, after draining or oth` erwiseeffecting removal of excess water therefrom, allowing it to age whilearranged in a relatively deep layer or layers for a period of the orderof 40 to 100 hours, preferably 50 to 75 hours.

To facilitate a clear understanding of the invention in its broad laswell as in its more specific aspects, the accompanying drawing shows aflow diagram illustrating a specific embodiment of the process asapplied to the prod-uction of fibrous pulp from a bagasse, for themanufacture of insulating board or the like.

In the practise of the invention according according to the embodimentillustrated and described, shredded bagasse as received from the sugarmill may be fed, as by means of a belt conveyor 11, to be dischargedinto the top of, and adjacent one end of a treating tank 12 in which itis to be soaked in an aqueous solution of soda ash or other suitable,weakly alkaline chemical. The aqueous solution of the chemical ispreferably made up in a separate solution tank 13, from which it may befed in desired quantities to the treating tank.

The treating solution is made up in the solution tank in a concentrationsuch that the amount of solution required fully to soak and saturate thebagasse delivered to treating tank 12 will provide, in the case of sodaash, an amount in the range of about 3 to 8 pounds, preferably 4 to 5pounds, for each 1,000 pounds of bagasse, calculated on the weight ofthe bagasse as received from the sugar mill.

In order to prevent the development and growth of fungus which mightotherwise occur during the period of ageing the treated bagasse, as moreparticularly hereinafter described, a suitable water-soluble fungicidemay be incorporated in the treating solution prepared in tank 13. Onesuitable fungicide which has been employed in the practise of theinvention is sodium pentachlorophenate, suoli yas that known by thetrade designation Dowicide G, sold by Dow Chemical Company.

The amount of this fungicide incorporated in the treating solution maybe such as to provide 0.4 to 0.8 pound thereof for each 1,000 pounds ofbagasse, calculated on the basis stated above with reference to theamount of soda ash used.

Desirably, treating tank 12 is provided with suitable agitator orpropelling means 14 arranged to thrust the bagasse into the treatingsolution and, at the same time move it toward the opposi-te end of thetank.

It is an advantage of the invention that suitable mechanism may also bearranged in the treating tank 12 whereby rock, metallic particles andother -abrasive substances intermixed with the raw bagasse may beseparated therefrom during the soaking treatment. For this purpose,suitably arranged baffles may be mounted in the tank, to separate therock etc., which may then be removed by an inclined Slat conveyor 16discharging onto a slat conveyor 22 extending transversely of the tankat the lower end 17 thereof. The rock etc. may be discharged into areceiving tank 23. By utilizing such separating means within thetreating tank, the excessive wear or damage to the working parts of thegrinders, refiners and pumps, utilized in preparing fibrous stock fromthe bagasse, and excessive wear upon the saws utilized for trimming theboard produced from the stock may be avoided or greatly minimized.Likewise, by such means, the likelihood of surface scratching of thepainted surface or decorative board may be minimized or eliminated.

After soaking in the treating solution in tank 12 for a period of two tothirty minutes, desirably two to five minutes, the soaked bagasse may beremoved from the tank by means of an inclined slat conveyor 15, passingover a perforated plate to permit liquid to drain away.

It appears from actual practise of the process, that the presence of `asubstantially more than about 80% by weight of water in the bagasse atthis stage accelerates the rate of hydration of the fibers during thesubsequent ageing step, to be hereinafter described. As a result, thefibrous stock produced from the aged material, though not muddy,exhibits lower than a desirable freeness for ready-de-watering of theformed sheets or wet mats by the presses of conventional board-formingmachines.

In order to avoid the aforementioned undesirable results of an excess ofwater during the ageing of the bagasse, the treated bagasse may bedischarged from conveyor into mechanism indicated at 18, suitablydesigned for squeezing excess water out of the bagasse. Preferably, thismechanism should serve to squeeze out sufiicient of the excess to reducethe amount of water which will be present during the ageing step to notsubstantially more than about by weight of the bagasse.

The treated bagasse, after squeezing out its contained excess water bymeans of mechanism 18, is then delivered to a suitable place forcarrying out the ageing step of the process.

Referring more in detail to the ageing step of the process, this iseffected, in accordance with the invention, by permitting the bagasse,after being soaked with the soda ash or other suitable chemical, asdescribed above, to age while maintained in quiescent state in `arelatively deep layer or layers for a period of time which may vary from40 to 100 hours, preferably about 50 to 75 hours, in an enclosed space,such as in a covered warehouse or in storage bins, indicated at 19. Thedepth of the layer or layers in which the material is left to age mayvary from 2 to 20 feet or more.

During the ageing cycle, there occurs an autogenous increase in thetemperature of the bagasse. In actual practise of the process, it hasbeen found that the ternperature reading, taken approximately one footbelow the surface of the pile of bagasse at the end of the first 24hours of the ageing period, was approximately 110 F., compared to anatmospheric temperature of 86 F. At the end of the second 24 hours ofthe ageing period, the temperature of the bagasse had increasedapproximately an additional 10 F., reaching approximately 120 F., or atotal increase of approximately 34 F., in fortyeight hours. At the endof the third 24 hours of the ageing cycle, however, no furthersubstantial rise in temperature of the bagasse was observed, and thetemperature remained substantially constant until the bagasse was readyfor use in the succeeding step in the production of pulp therefrom.

The autogenous increase in the temperature of the bagasse during theageing thereof, as above described, together with the chemical action ofthe soda ash or other treating chemical employed, effects a sufiicientsoftening .action upon the -lignin and other substances which bindtogether the bers or fiber lbundles of the bagasse, to conl dition thelatter for ready defibering and refining by con ventional grinders `andrefiners, for the formation of fibrous stock suitable for themanufacture of insulating board or the like. This conditioning of thebagasse by the process of the invention, aside from dispensing with theneed for high temperature cooking of the raw material, affords thefurther advantage, in many instances, of higher yields and improvedquality of fibrous stock, as compared to those obtained when utilizinghigh temperature digesting of the raw material.

Moreover, the process of the invention provides other importantadvantages. lt is known that when bagasse, in the damp condition(containing about 50% moisture) in which it is received from sugarmills, is stored for any substantial period of time, a noticeablyobnoxious, very pungent odor of acid fume prevails, evidently as aresult of enzyme action and fermentation. Also, the color of the bagasseturns brown, and this coloration is carried over to insulating board orthe like produced from pulp made from such bagasse.

Both of the foregoing difficulties, which arise when damp, untreatedbagasse is stored, are avoided in the present process wherein thebagasse is aged after being soaked with the aqueous solution of soda ashand Dowicide G. Furthermore, the presence of the latter prevents thedevelopment and growth of fungus in the form of mushrooms, as normallyoccurs when damp, untreated bagasse is stored.

Referring to the above-mentioned time period of ageing the bagasse, itmay be pointed out that the greater the ageing time, the greater is thetendency of the resultant fibers to lack the desirable degree ofspring-back in the sheet or wet mat produced therefrom, necessary forrapid de-watering of the sheet or mat on the presses of the formingmachine.

At the termination of the desired ageing, the bagasse may be conveyed bysuitable constant-feed mechanism, indicated at 24, to Bauer or otherconventional form of grinders 25 for defibering the treated bagasse.From the grinders, the pulp is fed to a decker 26 discharging into astock chest 27, from which it is delivered to a Clain or similar rener28 discharging into a stock chest 29. From the latter, the stock ispassed through a Jordan rener 30 and delivered to the board-formingmachine 31, such as an Oliver or Fourdrinier. After being formed intosheets, the latter are dried in drying ovens 32.

In actual practise, brous stock produced from the bagasse, in accordancewith the invention exhibited substantially the same board-formingcharacteristics as those of stock made from the bagasse when cooked bythe conventional process, and the iinished board produced from the pulpprepared in accordance herewith possessed substantially the samephysical properties and quality standards as those of the board producedfrom the cooked bagasse.

In the practise of the invention, provision may be made for blending thestock prepared from the bagasse treated and aged as above described,with desired amounts of stock prepared from raw and unaged bagasse, ininstances where the former is too slow as indicated by a freeness testeror is too soft and pliable to exhibit proper springback for normalde-watering in the presses of the boardforming machine. To that end, asindicated by dotted lines in the accompanying drawing, portions ofbagasse delivered by conveyor `11 may be diverted therefrom as by meansof a drop-gate to a stock-pile 33, from which desired quantities may beblended in the feeding device 24 with treated and aged bagasse.

What I claim is:

1. The method of forming fibrous stock for the production of berinsulating board from bagasse, which comprises soaking the bagasse atambient atmospheric temperature for a period of about two to thirtyminutes in an aqueous solution containing an alkaline treating chemicalin a concentration such that the amount of said solution required tofully saturate the bagasse will provide the equivalent of about 3 to 8pounds of soda ash per 1000 pounds of bagasse, reducing the aqueouscontent of the thus soaked bagasse to an amount not substantially inexcess of by weight of the bagasse, arranging the thus treated bagassein a relatively deep layer and permitting the same to age, while thusarranged, for a period of about 40 to 101) hours, during which periodthe temperature of the bagasse does not exceed approximately F., feedingthe thus aged bagasse directly from said layer to grinders for deberingthe same to a pulp, and

refining the ground pulp to form a brous stock suitable for theproduction of ber insulating board on a conventional board-formingmachine.

2. The method of claim 1, and wherein said solution also contains afungicidal agent in an amount suicient to prevent the development andgrowth of fungus during said ageing period.

3. The method ofrclaim 1, and wherein extraneous rock or other abrasivesubstance mixed with said bagasse is mechanically separated from thelatter during said soaking step.

4. The method of claim 1, wherein said agedV material is blended withbagasse which has not undergone said soaking and ageing treatment.

References Cited in the le of this patent UNITED STATES PATENTS 126,293Harang Apr. 30, 1872 1,627,103 Mason May 3, 1927 1,739,645 Munroe Dec.17, 1929 1,818,897 Kumagawa Aug. 11, 1931 2,899,350 Birdseye Aug. 11,1959

1. THE METHOD OF FORMING FIBROUS STOCK FOR THE PRODUCTION OF FIBERINSULATING BOARD FROM BAGASSE, WHICH COMPRISES SOAKING THE BAGASSE ATAMBIENT ATMOSPHERIC TEMPERATURE FOR A PERIOD OF ABOUT TWO TO THIRTYMINUTES IN AN AQUEOUS SOLUTION CONTAINING AN ALKALINE TREATING CHEMICALIN A CONCENTRATION SUCH THAT THE AMOUNT OF SAID SOLUTION REQUIRED TOFULLY SATURATE THE BAGASSE WILL PROVIDE THE EQUIVALENT OF ABOUT 3 TO 8POUNDS OF SODA ASH PER 1000 POUNDS OF BAGASSE, REDUCING THE AQUEOUSCONTENT OF THE THUS SOAKED BAGASSE TO AN AMOUNT NOT SUBSTANTIALLY INEXCESS OF 80% BY WEIGHT OF THE BAGASSE, ARRANGING THE THUS TREATEDBAGASSE IN A RELATIVELY DEEP LAYER AND PER-